pyfastmail-mcp

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states the tool retrieves emails but doesn't mention authentication needs, rate limits, pagination behavior, error conditions, or what 'Get' entails (e.g., read-only access, data format). For a tool with no annotation coverage, this leaves significant gaps in understanding its operational behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is front-loaded with the core purpose in the first sentence, followed by a concise parameter explanation. Every sentence earns its place—no fluff or redundancy. The structure is clear and appropriately sized for a simple tool.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's low complexity (2 parameters, no annotations, but has an output schema), the description is minimally adequate. It covers the purpose and parameters but lacks behavioral context (e.g., safety, performance). The presence of an output schema means return values are documented elsewhere, reducing the burden, but for a tool with no annotations, more guidance on usage and behavior would improve completeness.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 0%, so the description must compensate. It adds meaningful semantics: 'days' is explained as 'How many days back to look' with a default, and 'limit' as 'Max results' with a default. This clarifies the purpose of both parameters beyond their schema titles ('Days', 'Limit'), though it doesn't detail constraints like valid ranges or units.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool's purpose: 'Get emails received in the last N days.' It specifies the verb ('Get') and resource ('emails'), and the temporal scope ('last N days') distinguishes it from other mail tools like mail_search_emails or mail_get_email. However, it doesn't explicitly differentiate from all siblings (e.g., mail_list_mailboxes is clearly different, but the distinction from mail_search_emails could be more explicit).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives. It doesn't mention sibling tools like mail_search_emails (which might offer more flexible filtering) or mail_get_email (for specific emails), nor does it specify prerequisites or exclusions. The agent must infer usage from the purpose alone.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.